Methods for extracting power from sea water have been proposed for many years, most recently considered in a series of Ocean Thermal Energy Conversion (OTEC) Conferences which were sponsored by the Ocean System Branch Division of Central Solar Technology, U.S. Department of Energy, and published as proceedings of those Conferences. More than a century ago it was proposed to use the warm upper layer of the tropical ocean as a heat source and the cold deep water as a heat sink. To avoid the use of very large turbines operating in open cycle in the low vapor pressure of water at ambient temperatures the use in closed cycles of a working medium with a moderate vapor pressure at ambient temperatures, such as ammonia, was considered. Such systems, however, require expensive heat exchangers.
None of the many systems proposed has proved to be practical. They failed because they all require warm water flows, as large as 7450 Kg/Sec/MWe, massive structures to process them and vast, expensive heat transfer surfaces. These prior art systems need cold water pipes of excessively large diameter, about 57 feet per 100 MWe of electrical generating potential. Also, they are susceptible to biofouling by marine growth which reduces their heat transfer capacity.
It has long been known that ocean water contains dissolved gases, typically oxygen, nitrogen and carbon dioxide. When these dissolved gases come out of solution from ocean water in a conduit they form a foam which has a lower bulk density than that of the water with dissolved gases and is therefore more buoyant. However, prior to the present invention, the art has not recognized that this phenomenon can be utilized to produce energy. Indeed, the presence of dissolved gases in surface and cold deep ocean water used in OTEC systems has been considered to be undesirable. In such systems one must remove the non-condensible gases to raise the dew point of the water vapor to a temperature above 40.degree. F to effect condensation of the water vapor.
Consequently, there is a need for a low cost system for producing energy from ocean water which has no significant susceptibility to bio-fouling and in which dissolved gases have no detrimental effects.